Communications networks are being used increasingly widely for measuring complex technical systems and for open-loop and closed-loop control of the systems. For example, networks are being used increasingly in motor vehicles in order to develop vehicle control systems. In corresponding complex and safety-relevant technical systems, high demands are placed on the availability of the control elements provided as network devices. The failure of individual components such as sensors or control devices, for instance, must not result in the failure of the entire system. Drive-by-wire systems are relevant to safety, in which electric motors are used to convert the steering-wheel position into wheel positions via a network-coupling of sensors, control devices and actuators.
In these systems, data is commonly exchanged via a packet-based communications network in such a way that in the event of a single error in the communications network, the data arrives without loss of information. For example, data may be sent more than once from a source node to a destination node so that the data may be received reliably even when there is a network fault. The HSR protocol (High-availability Seamless Redundancy), for instance, is known for Ethernet applications. HSR requires the network to have a ring topology, however, which is fundamentally problematic for Ethernet networks. The likewise known PRP (Parallel Redundancy Protocol) requires two parallel networks.
In particular, for networks that are based on the Ethernet standard, ring topologies may only be implemented at high cost. U.S. 2010/0020809 A1 defines a method in which a virtual local area network (VLAN) in an Ethernet network is organized as a ring topology. In this method, each node is assigned a switch that breaks the ring at a suitable point and operating situation.
It is desirable to operate data communication, and, in particular, data communication based on an Ethernet structure, with a higher degree of error protection. Normally, this requires the implementation of two disjunctive communications paths from a data source to a destination node.